What MPG are you getting?

jsmusic

jsmusic

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Joined
Sep 10, 2022
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7
Location
Raleigh, NC
Hey all.

Just read a thread about folks getting 17mpg and 18mpg in their TJs.

I have a 4.0, auto, running a 3.5” lift and 31s. Tires are bf goodrich mudterrains.

My average mpg is 10mpg, with 11.5mpg being my highest. That was me doing everything I could to keep in the overdrive “gear” with RPMs below 3k.

When I read the higher mpgs, got me thinking - is something wrong / old with mine? I do know I need a track bar replacement as well as the steering stabilizer replaced. Maybe that’s creating extra work?

Thanks all,

J
 
10-11 does seem low with your set up. Mine gets 13.5-14.5 MPG w/ city/country road mix (4.6L stroker, AX-15, 33X12.50 and 4.11 gears). Interestingly, it was about 1 MPG lower before I changed my rear Trutrac to an e-locker (less parasitic loss when fully open? 🤷‍♂️)
 
The following are things that will effect gas mileage; driving as speeds above 60 mph, engine is operating below the recommended factory temperature, lower tire pressure, brake shoes dragging slightly, old O2 sensors are to name just a few of the more common ones.

My '01 4.0L 5 speed w/ 2" lift, 32's and 4.11s gets 18 mpg highway which is down from 20 mpg since I went to 4.11s (yes I calibrated the speedo), but I drive 70-75 mph on the highway instead of 60 which would be better when trying to squeeze out more MPG.
 
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My '00 4.0L 5 speed w/ 2.5" lift, 33's and 3,73's gets 13.8mpg average (uncorrected speedo gear) in the last 14 months. Mostly highway.

Next week it gets 4.56's and corrected speedo gear so... who knows...
 
‘06 Unlimited with auto and the same 31” BFG mud terrains and I get 12 around town. 17 is the best I got on the highway loaded down and using cruise control.

When driving around town, I turn the O/D off. Sometimes on 55-60 mph roads too. On the interstate I leave the O/D on.
 
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Yes your 2003 has the 42RLE automatic, that particular transmission drops the rpms so low on the highway that it can cause the engine to lug and get bad mpg.

Do you know what axle ratio is installed? 3.07 or 3.73? If you don't know you can look at the steel tag with your ratio embossed into it at the 9 o'clock position on your differential cover. This one is indicating 3.73 gears are inside the axle. A 3.07 ratio would cause excessively low rpms on the highway which can wreck the mpg, 3.73 isn't far behind with that problem though... all due to how low the 42RLE's .69 Overdrive ratio drops the rpms on the highway.

Axle Ratio.jpg


And are you detecting the aroma of gasoline when you're in or around your TJ when it's running? That can indicate the engine is running too rich which will definitely reduce the mpg.
 
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jsmusic said:
I have a 4.0, auto, running a 3.5” lift and 31s.
Click to expand...

I curious about what axle ratio too.

I'm running a 4.0, 5 speed, 4.10 and 33" and get 12-15. I tend to average 12.5 city and highway driving, and I get 15 cruising the back roads in the 45-60 mph zone.

Edited to add axle ratio that I somehow forgot to include.
 
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got 13 on strict highway driving yesterday (60-70mph). combined driving I get 10-11. 33" 4.56 gears on 5speed. Not great
 
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